import java.util.HashMap;
import java.util.Hashtable;
import java.util.concurrent.ConcurrentHashMap;

/**
 * @author zhu_shuai
 * @since 2021/6/20
 */
public class MapDemo {
    public static void main(String[] args) {
        Hashtable hashtable = new Hashtable();
        hashtable.put("a", 1);
        HashMap<Object, Object> hashMap = new HashMap<>();
        hashMap.put("a", 1);
        ConcurrentHashMap concurrentHashMap = new ConcurrentHashMap();
        concurrentHashMap.put("a", 1);
    }
}
